This paper deals with the utilization of a natural pozzolan as the main component of Hydraulic Road Binder (HRB). A study of its reactivity in presence of lime and gypsum leads to a proposal for an optimized binder composed of 80 wt% pozzolan, 15 wt% lime and 5 wt% gypsum. The characteristics of this binder were tested on mortars and on samples of treated soil and the results lead to the conclusion that it is possible to produce an HRB rich in pozzolan and without cement that can efficiently stabilize clayey soils. (C) 2012 Elsevier Ltd. All rights reserved.